1. Carbon black
Carbon black appears as chain-like or grape-like structures under a scanning electron microscope, with each individual carbon black particle possessing a very large specific surface area (700 m²/g). The high specific surface area and dense packing of carbon black particles facilitate close contact between them, forming a conductive network in the electrode. However, the large specific surface area presents processing challenges, including difficulty in dispersion and strong oil absorption. This necessitates improving the mixing process of the active material and conductive agent to enhance dispersibility, while controlling the carbon black content within a certain range (typically below 1.5%). The morphology of carbon black and its mixing state in the active material are shown in Figure 1.
2. Conductive graphite
Conductive graphite also has good conductivity. Its particles are close to the particle size of living matter, and the particles are in point contact with each other, which can form a conductive network structure of a certain scale. This can improve the conductivity rate and increase the capacity of the negative electrode when used as a negative electrode.
3. Carbon fiber (VGCF)
Conductive carbon fibers possess a linear structure, readily forming a good conductive network within the electrode, exhibiting superior conductivity. This reduces electrode polarization, lowers battery internal resistance, and improves battery performance. Inside the battery where carbon fiber serves as the conductive agent, the contact between the active material and the conductive agent is point-to-line, which, compared to the point-to-point contact between conductive carbon black and conductive graphite, not only improves electrode conductivity but also reduces the amount of conductive agent required, thereby increasing battery capacity. Figure 2 shows a comparison of the dispersion states of VGCF and conductive carbon black in the active material.
4. Carbon nanotubes (CNTs)
Carbon nanotubes (CNTs) can be divided into single-walled and multi-walled CNTs. One-dimensional carbon nanotubes, similar to fibers, are long, columnar with a hollow interior. Using carbon nanotubes as conductive agents allows for the formation of a well-developed conductive network, and their contact with the active material is point-to-line. This has significant applications in improving battery capacity (increasing electrode compaction density), rate performance, battery cycle life, and reducing interfacial impedance. Currently, BYD and CALB use CNTs as conductive agents in some products, with positive results. Carbon nanotubes can be grown in two forms: entangled and arrayed. Regardless of the form, dispersion is a challenge when applied to lithium-ion batteries. This can be addressed through processes such as high-speed shearing, adding dispersants, creating dispersion slurries, and electrostatic dispersion using ultrafine grinding beads.
5. Graphene
Graphene, as a novel conductive agent, has a unique sheet-like structure (two-dimensional structure) that allows for point-to-surface contact with active materials rather than the conventional point-to-point contact. This maximizes the application of the conductive agent, reduces the amount of conductive agent used, and thus allows for the use of more active materials, thereby increasing the capacity of lithium-ion batteries. However, due to its high cost, difficulty in dispersion, and potential obstacles to lithium-ion transport, it has not yet been fully industrialized.
6. Binary and ternary conductive pastes
In the latest research progress, some lithium-ion batteries use conductive agents that are mixtures of two or three of CNTs, graphene, and conductive carbon black. The creation of conductive slurries by combining conductive agents is a requirement for industrial applications and a result of the synergistic effects between the conductive agents. Whether it's carbon black, graphene, or CNTs, dispersing them individually is already quite difficult. If you want to uniformly mix them with active materials, you must disperse them before stirring the electrode slurry and then use them.
